Aluminum potroom work has been associated with respiratory illness including increased non-specific bronchial hyperresponsiveness (NSBR), asthma-like symptoms and air flow obstruction in cross- sectional studies. However, the studies are hampered by the lack of health data on workers prior to exposure and are susceptible to survivor bias in the data analysis. This prospective cohort study will test the hypothesis that potroom exposures result in increased NSBR, new asthma-like symptoms, and occupational asthma, by collecting symptom, pulmonary function and methacholine challenge data on an inception cohort of aluminum workers, before and after exposure to the potroom. Case definitions will be used to identify incident cases of asthma-like symptoms, increased NSBR, or occupational asthma. Peak Flow measurements will be used to determine the work- relatedness of these outcomes. Host risk factors for developing respiratory outcomes and data on exposure.response relationships will be analyzed as predictors for outcomes. This prospective study of an inception cohort will detect incident cases for asthma outcomes with repeat measurements in an already assembled cohort of aluminum potroom workers, while minimizing the chance for survivor bias.